Summary

It has been widely accepted since Carnot's seminal work (1) that the atmosphere acts as a thermodynamic heat engine: Air motions redistribute the energy gained from the Sun in the warm part of the globe to colder regions where it is lost through the emission of infrared radiation to space. Through this process, some internal energy is converted into the kinetic energy needed to maintain the atmospheric circulation against dissipation. The analogy to a heat engine has been applied to explain various atmospheric phenomena, such as the global circulation (2), hurricanes (3), and dust devils (4). On page 540 of this issue, Laliberté et al. (5) show that the hydrological cycle reduces the efficiency of the global atmospheric heat engine.